Signaling apparatus for telephone systems



Apr. 17, 1923.

M. L. NELSON SIGNALING APPARATUS FOR TELEPHONE SYSTEMS [I ffm Filed June 13, 1921 Patented Apr. 17, 1923.

UNITED STATES PATENT OFFICE.

MARTIN L. NELSON, O13 CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

7 Application filed June 13, 1921. Serial No. 477,268.

To all wiwm it may cmwern:

Be it known that I, MARTIN L. NELSON, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Signaling Apparatus for Telephone Systems, of which the following is a specification.

This invention relates in general to signaling apparatus for telephone systems, and especially to apparatus of this character which is used for producing audible busy signals and other similar signals in automatic or manual telephone systems. The apparatus herein shown is especially designed for use in automatic telephone systems, but is also adapted for use in manual systems.

The object of the invention is to provide audible signaling equipment of the character designatedwhich will produce clear, uniform and distinct signals, which is economical to manufacture, and which will operate continuously for long periods with a minimum of attention.

The invention will be described with reference to the accompanying drawings, in which Fig. 1 shows a b si aling machine which is adapted to rnish busy signaling currents of two difierent volumes, one for use at the connector boards in an automatic telephone system, and the other for use at the trunk boards. Fig. 2 shows a signaling machine which is intended to furnish the characteristic dial tone whereby callin automatic subscribers are notified that t ey have obtained access to directively controllable automatic switches and that they may, therefore, proceed to operate their calling devices.

Referring to Fig. 1, the signalin machine therein shown is one of two dup icate sets which are ordinarily rovided for an exchan The common eads 2 and 3 supply the signaling current generated by the machine to the connector and trunk switchboards, respectivel and when the switch S is closed these lea s are connected with the signaling machine shown by way of leads 4 and 5. The leads 6 and 7 correspond to the leads 4 and 5 and extend to the other machine of the set. It will be clear that if the other set is to be used instead of the one which is shown in the drawing, switch S will be closed and switch S will be opened.

The essential parts of the set shown in Fig. 1 are the buzzer, the ma net coils of which are indicated bythe re erence character 15; the transformer R; and the relay interrupter comprising relays 20, 21, and 22. The buzzer is provided with an armature '16 which consists of a heavy steel spring, whereby the buzzer is caused to operate at a very high frequency. The

transformer R has its primary winding included in a local circuit with the buzzer and the battery, while its secondary winding is in series with the common signaling leads 4 and 5. The relay interrupter is provided in order to produce the characteristic intermittent buzz of the busy tone. When the set is in use the relays energize and deenergize in continuous succession, and relay 2O intermittently short circuits the secondary winding of the transformer R.

In order to have the machine operate with the maximum eliiciency it is essential that the various condensers, retard coils, etc., have values which are in correct proportion to each other. The table below gives certain values which have been determined by experiment to be very satisfactory, but it is to be understood that these may be modified if desired, and the invention is, therefore, not limited to the precise figures indicated. The values given are'for operation on a fortyeight volt battery.

Buzzer ma net 15 800 ohms. Non-induct ve resistance 18; 600 Condenser 17 .04 micro-feuds. Retardation coil 12 200 ohms. Resistance 19 15o Retardation coil 9 C 8 2 micro-funds. Primary winding 10 ct transformer B- 5401mm.

13. retardation coil 12, primary winding 10 of the transformer R, conductor 17, winding of the buzzer magnet 15, a section of conductor 14, and through the lower switch blade to the positive pole of the battery. Magnet 15 is energized over the above traced circuit and the buzzer consequently begins to operate, since the armature thereof short circuits the magnet winding every time it is attracted, and by induction between the two transformer windings high frequency cur-- rent is induced in the secondary winding 11.

At the same time that the local circuit is closed for the buzzer the relay interrupter is set'in motion. When the battery is connected across conductors 13 and 14 circuits are closed simultaneously for all three of the relays 20, 21, and 22. Relay 20, having more contact springs to operate than either of the other relays, will not energize quite as quickly as the other two. Relay 21, whose circuit is controlled by relay 20 at armature 25, will completely energize, but relay 22, although it may start to pull up, will immediately fall back as soon as its circuit is opened at armature 26 of relay 21. At the initial closure of the circuit, therefore, relay 21 will become fully energized. An instant later relay 20 will operate, whereupon the circuit of relay 21 is broken at armature 25. Upon deenergizing, relay 21 closes the circuit of relay 22 at armature 26. Upon energizing, relay 22 breaks the circuit of relay 20 at armature 27. Relay 20 now falls back and at armature 25 again closes the circuit of relay 21. These operations, in which the relays are energized alternately, will continue indefinitely, or as long as the circuit remains closed, and it will be seen, therefore, that relay 20 will periodically short circuit the secondary winding 11 of the transformer R at the back contact of its armature 24. This operation periodically stops the generation of signaling current and produces the well known charactertistic busy buzz. In actual practice the retardation coil 9 is usually mounted quite close to the transformer R, and in order to prevent the generation of weak signaling current by stray magnetic flux this coil is shorted out also by means of armature 23.

The manner in which the busy signaling currents are applied to a calling subscrihers line in order to give himthe required audible signal is well known and need not be described in detail. The conductor 2 is multiplied into all of the connector boards and supplies busv signaling current to notify subscribers that the called lines are busy. It will be observed that the circuit for the common conductor 2 includes the condenser 8 and retardation coil 9. The condenser is included in order to prevent any How of direct current over the circuit, while the retardation coil 9 is added in order to reduce extends to all of the selector boards in the exchange and provides signaling current for giving a calling subscriber a busy signal in case all outgoingtrunks of the selected group are busy. The use of busy signaling current for this purpose is described in the U. S. Patent to Jacobsen No. 1,352,605, granted September 14, 1920.

Referring now to Fig. 2, the apparatus shown therein comprises a duplicate set of dial tone machines. which, as before stated, are used for supplying signaling currents for giving the characteristic dial tones to calling subscribers, these dial tones being audible signals which advise the calling subscribers that they may begin to operate their calling devices. The use of signals of this character is described in the patent to Jacobsen above referred to.

In view of the explanation of the busy signaling equipment shown in, Fig. 1, it will be unnecessary to go into minute details with regard to the apparatus shown in Fig. 2. The buzzer 52 is substantially like the buzzer 15 except thatit is arranged to vibrate with a different frequency in order to generate a different characteristic tone. When the double pole double throw knife switch 5 is closed the buzzer 52 begins to operate. The single pole single throw switch S may now be closed and a signaling current will be generated in the secondary winding 54 of the transformer R by inductive action between the said winding and the primarywinding 53. The common conductor 50 extends to the first selector boards where it is multiplied to the various switches, as illusitrated in the Jacobsen patent above cite It will be understood that in the case of the dial .tone apparatus, both of the duplicate sets which are commonly used are shown in the drawing. The apparatus just described constitutes the first set and is placed in operation by the closure of switches S and S as described, while the apparatus immediately below constitutes the second set and is placed in service by the closure of switches S and S Ill It will be observed that in the case of the ing said secondary winding.

2. In a signaling system, a common signal' conductor, a transformer having a secon ary winding in series with said conductor, a local circuit including a magnet and the primary windin of said transformer, an armature for said magnet adapted to short circuit the magnet winding to cause said magnet to operate as a buzzer, a relay interrupter comprising a series of relays, each relay being adapted to open the tardation coil include circuit of the next relay in the series, and

by one of said contacts closed periodicallyl d d a 581 S600)! flly relays for short circuiting t winding.

3. In a signaling system, a common signaling conductor havin two branches, a rein one branch, a transformer having a secondary winding in series with the undivided ortion of said conductor, a local circuit inc uding a buzzer and a primary winding of said transformer, a relay interrupter and circuit connections for energizing the relays of said interrupter in continuous succession, contacts actuated periodically b one of said relays for shortcircuiting sai secondary winding, and other contacts actuated by the same relay at the same time for short circuiting said retardation coil.

Ingwitness whereof, I hereunto subscribe my name this 3rd day of June, A. D., 1921.

MARTIN L. NELSON. 

